Mollusca of Great Britain. 371 



amphibious, since the nature of their food frequently obliges 

 them to seek it on wet and marshy ground. During the 

 spring they are greatly infested by a minute slender spe- 

 cies of Gordius, which in number from two to ten attach 

 themselves to the interior of the mantle near its connection 

 with the neck of the animal. Draparnaud called them fila- 

 mentary organs, and supposed that they performed the office 

 of tentacula, probably from seeing them always in motion 

 and appearing to issue from the back of the head. This 

 troublesome parasite does not seem to be stationary, since 

 I have not unfrequently observed it to change its place and 

 take up perhaps more commodious quarters in another shell. 

 It probably constitutes part of the food of the smaller Dy- 

 tiscidce. Afterlhadput two sorts (the D.^rj^i/Ms, and D.cras- 

 sicornis, M.) into the glass vessel where the Limnei were 

 kept, I could not detect any signs of the Gordii ; though 

 in other cases I have known them to survive even after 

 their guardians had begun to putrefy. 



The food of the Limnei is animal and vegetable matter in 

 different states of putridity ; which makes them deserve the 

 perhaps not inapt epithet of " Scavengers of the waters." 

 In the absence of other nourishment they will even devour 

 each other, piercing the shell near its apex, and eating away 

 the upper folds of its inhabitant. This accounts for the 

 mutilated and often imperfectly repaired state of the upper 

 volutions of some specimens. 



* Umbilico nullo, perislomio non rejlexo. 



1. Glutinosus. 



Animal lubricum, viscidum, album, punctis sparsum ci- 



nereis : pallio gelatinoso spiram obtegente. {Miill.) 

 Testa subglobosa, ventricosa, nitida, diaphana, fragilis- 



sima. 



